Puntarenas, Costa Rica – An international team of scientists has just returned from an ocean drilling expedition on board the JOIDES Resolution, near the Pacific coast of Costa Rica, designed to study the subduction zone where the Cocos tectonic plate dips beneath the Caribbean plate. This fault boundary was responsible for causing two earthquakes earlier this year, on September 5 and October 23. While the epicenter of those quakes was north of the study site, under the Nicoya Peninsula, the samples and data collected offshore will help scientists better understand how earthquakes happen – here in Costa Rica and elsewhere.

Integrated Ocean Drilling Program (IODP) Expedition 344 (Costa Rica Seismogenesis Project A Stage 2), also known as CRISP 2, picked up where Expedition 334 (CRISP 1) left off last year. The study site, near the Osa Peninsula, is of particular interest for two major reasons. First, it is a relatively shallow subduction zone, and such boundaries are responsible for some of the world’s deadliest and most damaging earthquakes and tsunamis. Second, the boundary is an erosive convergent margin, a type that is relatively poorly understood by scientists.

“There are a lot of subduction zones where we could drill – and have drilled – to study earthquake processes. However, the Cocos-Caribbean margin represents a particularly strategic opportunity to learn about shallow, erosive margins,” says co-chief scientist Robert Harris of Oregon State University. “What we learn here could potentially frame new research questions for decades to come.”

In contrast to accretionary convergent margins, which transfer sediments to the overlying plate as the subducting plate travels deeper, erosive margins like the Cocos-Caribbean boundary drag large amounts of sediment into the Earth’s interior. Because this process removes mass from the upper plate, it can cause the overlying ground to subside, potentially generating seismic activity. While accretionary margins have been studied more extensively, scientists still have much to learn about erosive margins. Drilling into these zones is the only way to directly observe the processes responsible for damaging seismic activity.

The expedition left from Panama on October 23 and concluded in Puntarenas on December 11. The team drilled 10 boreholes, each of which penetrated from 25 to 800 meters into the ocean floor. Core samples, as well as data recorded from the borehole walls using sensitive instruments lowered into the holes, will help the team characterize the geophysical and chemical properties of the seismogenic zone. In total, the team recovered more than one and a half kilometers of core.

To read more please visit: OceanLeadership.org